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<title>Boilerplate code: GObject Reference Manual</title>
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<div class="sect1">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="howto-gobject-code"></a>Boilerplate code</h2></div></div></div>
<p>
      In your code, the first step is to <code class="function">#include</code> the
      needed headers:
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
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        <td class="listing_lines" align="right"><pre>1
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        <td class="listing_code"><pre class="programlisting"><span class="comment">/*</span>
<span class="comment"> * Copyright information</span>
<span class="comment"> */</span>

<span class="gtkdoc ppc">#include</span> <span class="gtkdoc pps">&quot;viewer-file.h&quot;</span><span class="gtkdoc ppc"></span>

<span class="comment">/* Private structure definition. */</span>
<span class="gtkdoc kwc">typedef</span> <span class="gtkdoc kwb">struct</span> <span class="gtkdoc opt">{</span>
  gchar <span class="gtkdoc opt">*</span>filename<span class="gtkdoc opt">;</span>
  <span class="comment">/* stuff */</span>
<span class="gtkdoc opt">}</span> ViewerFilePrivate<span class="gtkdoc opt">;</span>

<span class="comment">/* </span>
<span class="comment"> * forward definitions</span>
<span class="comment"> */</span></pre></td>
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<p>
    </p>
<p>
      If the class is being declared as final using
      <code class="function">G_DECLARE_FINAL_TYPE</code>, its instance structure should
      be defined in the C file:
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
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        <td class="listing_lines" align="right"><pre>1
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6</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">struct</span> _ViewerFile
<span class="gtkdoc opt">{</span>
  GObject parent_instance<span class="gtkdoc opt">;</span>

  <span class="comment">/* Other members, including private data. */</span>
<span class="gtkdoc opt">}</span></pre></td>
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</div>

<p>
    </p>
<p>
      Call the <code class="function">G_DEFINE_TYPE</code> macro (or
      <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> if your class needs
      private data — final types do <span class="emphasis"><em>not</em></span> need private data)
      using the name
      of the type, the prefix of the functions and the parent GType to
      reduce the amount of boilerplate needed. This macro will:

      </p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">implement the <code class="function">viewer_file_get_type</code>
        function</li>
<li class="listitem">define a parent class pointer accessible from
        the whole .c file</li>
<li class="listitem">add private instance data to the type (if using
        <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>)</li>
</ul></div>
<p>
    </p>
<p>
      If the class has been declared as final using
      <code class="function">G_DECLARE_FINAL_TYPE</code> (see
      <a class="xref" href="howto-gobject.html#howto-gobject-header" title="Boilerplate header code">the section called “Boilerplate header code”</a>), private data should be placed in
      the instance structure, <span class="type">ViewerFile</span>, and
      <code class="function">G_DEFINE_TYPE</code> should be used instead of
      <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code>. The instance structure
      for a final class is not exposed publicly, and is not embedded in the
      instance structures of any derived classes (because the class is final);
      so its size can vary without causing incompatibilities for code which uses
      the class. Conversely, private data for derivable classes
      <span class="emphasis"><em>must</em></span> be included in a private structure, and
      <code class="function">G_DEFINE_TYPE_WITH_PRIVATE</code> must be used.

</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
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        <td class="listing_lines" align="right"><pre>1</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE:CAPS">G_DEFINE_TYPE</a></span> <span class="gtkdoc opt">(</span>ViewerFile<span class="gtkdoc opt">,</span> viewer_file<span class="gtkdoc opt">,</span> G_TYPE_OBJECT<span class="gtkdoc opt">)</span></pre></td>
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</div>

<p>
or
</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="function"><a href="gobject-Type-Information.html#G-DEFINE-TYPE-WITH-PRIVATE:CAPS">G_DEFINE_TYPE_WITH_PRIVATE</a></span> <span class="gtkdoc opt">(</span>ViewerFile<span class="gtkdoc opt">,</span> viewer_file<span class="gtkdoc opt">,</span> G_TYPE_OBJECT<span class="gtkdoc opt">)</span></pre></td>
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</div>

<p>
    </p>
<p>
      It is also possible to use the
      <code class="function">G_DEFINE_TYPE_WITH_CODE</code> macro to control the
      <code class="function">get_type</code> function implementation — for instance, to
      add a call to the <code class="function">G_IMPLEMENT_INTERFACE</code> macro to
      implement an interface.
    </p>
</div>
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